1. Field of the Invention
The present invention relates to a power slide device for a vehicle seat.
2. Description of Related Art
FIG. 9 shows an example of a power slide device, according to the related art, for a vehicle seat.
This power slide device is provided with a lower rail 01, an upper rail 02, a screw rod 03 and a gear box 04. The lower rail 01 is fixed to a vehicle floor and extends in the forward/rearward direction (horizontal direction with respect to FIG. 9), the upper rail 02 is slidable relative to the lower rail 01 in the forward/rearward direction, the screw rod 03 is fixed to the lower rail 01 and extends in the forward/rearward direction, and the gear box 04 is fixed to the upper rail 02. The gear box 04 is equipped with a worm wheel (not shown) which rotates by the driving force of a motor (not shown). The screw rod 03 is screw-engaged into a female screw hole, which formed in the worm wheel as a through-hole extending in the forward/rearward direction.
A front support member (not shown) is fixed to the front of the lower rail 01 and supports the front of the screw rod 03. On the other hand, a rear support member 05 which is L-shaped in cross section is fixed to the rear of the lower rail 01. The rear support member 05 is provided with a substantially horizontal fixed portion 06 that is fixed to the lower rail 01 and a rear orthogonal (upright) plate portion 07 which extends upward from the front end of the fixed portion 06, and a through-hole 08 through which the screw rod 03 extends is formed in the rear orthogonal plate portion 07. Screwing two nuts 09 and 010 that are positioned behind and in front of the rear orthogonal plate portion 07 onto the screw rod 03 so as to sandwich and hold the rear orthogonal plate portion 07 between the front surface of the nut 09 and the rear surface of the nut 010 from the front and rear sides, respectively, makes the rear support member 05 fixedly support a portion of the screw rod 03 in the vicinity of the rear end thereof.
Accordingly, rotating the worm wheel in the forward direction by a forward rotation of the aforementioned motor causes the worm wheel and the upper rail 02 to move forward relative to the lower rail 01 and the screw rod 03, while rotating the worm wheel in the reverse direction by a reverse rotation of the aforementioned motor causes the worm wheel and the upper rail 02 to move rearward relative to the lower rail 01 and the screw rod 03.
If a vehicle equipped with this power slide device comes into collision with another vehicle ahead from behind, a forward inertia force acts on the upper rail 02 (and also on the seat fixed to the upper rail 02), and accordingly, a forward force acts on the screw rod 03 from the worm wheel.
Consequently, the screw rod 03 attempts to move forward relative to the rear support member 05. However, if this inertia force is smaller than a predetermined value, the screw rod 03 is prevented from moving forward by the rear support member 05 (the rear orthogonal plate member 07), so that the screw rod 03 and the rear support member 05 are maintained in the same state (shape) as before the collision.
Another example of the related art is disclosed in Japanese Unexamined Patent Publication No. 2004-210174.
However, when the aforementioned inertia force, which is caused by a collision of vehicle equipped with the power slide device occurring, is great (i.e., greater than the aforementioned predetermined value), the connecting portion between the fixed portion 06 and the rear orthogonal plate portion 07 is plastically deformed, which causes the rear orthogonal plate portion 07 to tilt forward about the connecting portion, thus causing the screw rod 03 that is supported by the rear orthogonal plate portion 07 to be deformed.
If the rear support member 05 is plastically deformed and the screw rod 03 is also deformed (plastically deformed) in the above-described manner, the power slide device no longer be actuated thereafter.